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United States Patent |
5,147,599
|
Mansson
|
September 15, 1992
|
Fuel assembly of a nuclear reactor
Abstract
A fuel assembly for a nuclear reactor with a number of parallel fuel rods
which are retained by means of spacer lattices and guide tubes (3), which
guide tubes (3) are also fixed to the spacer lattices, a top tie plate (4)
and a bottom tie plate between which the guide tubes (3) with associated
fuel rods are fixed. The top tie plate (4) has been provided with
through-holes (10) for connection to a top sleeve (7) joined to the upper
end surface of the respective guide tube (3). According to the invention,
there is arranged inside the top sleeve (7) a first locking element (9)
for cooperation with a second locking element (13). This is arranged on a
guide sleeve (11) which is insertable through a hole (10) in the top tie
plate (4), which hole corresponds to the respective top sleeve (7).
Inventors:
|
Mansson; Ragnar (Vaster.ang.s, SE)
|
Assignee:
|
ABB Atom AB (Vaster.ang.s, SE)
|
Appl. No.:
|
665317 |
Filed:
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March 6, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
376/446; 376/441; 376/449 |
Intern'l Class: |
G21C 003/32 |
Field of Search: |
376/446,449,441,442,440
976/DIG. 65,DIG. 68
|
References Cited
U.S. Patent Documents
3864211 | Feb., 1975 | King et al. | 376/440.
|
4064004 | Dec., 1977 | Long et al. | 376/440.
|
4699759 | Oct., 1987 | Feild, Jr. | 376/446.
|
Primary Examiner: Hunt; Brooks H.
Assistant Examiner: Chelliah; Meena
Attorney, Agent or Firm: Watson, Cole, Grindle & Watson
Claims
I claim:
1. A fuel assembly for a nuclear reactor which comprises a top tie plate
which has a top surface, a bottom surface and a hole which extends
therethrough from said top surface to said bottom surface, a bottom tie
plate, a plurality of parallel fuel rods which extend between said top tie
plate and said bottom tie plate, a plurality of spacer lattices positioned
along said fuel rods, a plurality of guide tubes located between said fuel
rods, said guide tubes being fixed to said spacer lattices, a seat in said
top tie plate around said hole, a top sleeve which defines a lower end to
which an upper end of a guide tube can be joined and an upper end which
abuts said seat, a first locking means inside said top sleeve, a guide
sleeve which is positionable through said hole in said top tie plate and
into said top sleeve, and a second locking means on the outside of said
guide sleeve which is cooperable with said first locking means to connect
said guide sleeve and said top sleeve together.
2. A fuel assembly according to claim 1, wherein said hole through said top
tie plate has a first part which extends from said top surface towards
said bottom surface and a second part which extends from said first part
to said bottom surface, said second part having a larger diameter than
said first part, said diameter of said second part corresponding to an
outer diameter of the upper end of said top sleeve and providing said
seat.
3. A fuel assembly according to claim 1, wherein said first locking means
comprises an inner slot which extends around a circumference of said top
sleeve.
4. A full assembly according to claim 3, wherein said second locking means
comprises an external bead which extends around the periphery of said
guide sleeve, said bead being positionable in said inner slot of said top
sleeve, and wherein said guide sleeve includes an axial slit to enable
said bead to be positioned within said inner slot.
5. A fuel assembly according to claim 1, wherein said guide sleeve includes
a flange that abuts said top surface of said top tie plate.
6. A fuel assembly according to claim 1, including a locking sleeve which
is positionable within said guide sleeve to interlock said guide sleeve to
said top sleeve.
7. A fuel assembly according to claim 6, wherein said locking sleeve is
provided with a swelling which fits the indentation formed inside the
guide sleeve on the back of its external bead or below the end of the
guide sleeve.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a fuel assembly for a nuclear reactor with
a detachable top tie plate to make possible reconditioning of the fuel
assembly.
A fuel assembly of a known design comprises a plurality of fuel rods and
guide tubes for control rods or arranged as water tubes only in certain,
special nuclear reactors, the fuel rods and guide tubes being kept in
predetermined mutual positions by means of spacer lattices placed along
the fuel assembly. The top tie plate and the bottom tie plate at the ends
of the fuel assembly are fixed to the guide tubes of the control rods,
which guide tubes extend somewhat above and below the ends of the fuel
rods. In this known fuel assembly the guide tubes are provided on top with
a top sleeve which fits into a corresponding hole through the top tie
plate. A peripheral slot is arranged in the hole, a bead around the upper
part of the top sleeve fitting into this slot. The top sleeve is provided
with an axial slit, extending from its upper end through the bead and made
of a resilient material The slit permits the upper end of the top sleeve
to be squeezed together so that the top sleeve can be moved in the hole of
the top tie plate to a position in which the bead falls into the slot,
whereupon the end is allowed to rebound. To ensure the locking between the
top sleeve and the top tie plate, a locking sleeve is inserted into the
top sleeve, which locking sleeve prevents the bead from leaving the slot.
A drawback of this design is that a rather extensive machining of the top
tie plate must be performed, such as, for example, milling of slots in the
holes. Further, when mounting the top tie plate, all top sleeves must be
squeezed together more or less simultaneously in order for the top tie
plate to be fitted onto the top sleeve. Accordingly, this mounting may
become quite problematic.
SUMMARY OF THE INVENTION
The present invention avoids the above-mentioned drawbacks. As usual, the
fuel assemby comprises a number of parallel fuel rods which are retained
by means of spacer lattices, arranged along the fuel rods, as well as
guide tubes for control rods or arranged only as water tubes in certain,
special nuclear reactors. The guide tubes are arranged between the fuel
rods and fixed to the spacer lattices. The guide tubes and the associated
fuel rods have been fixed between a top tie plate and a bottom tie plate.
The top tie plate has been provided with a through-hole for connection of
a top sleeve joined to the upper end of the guide tubes.
According to the invention, there is arranged inside the top sleeve a first
locking element intended to cooperate with a second locking element
arranged on a guide sleeve, which is insertable through a hole in the top
tie plate, which hole corresponds to the top sleeve.
By the invention, extra machining of the top tie plate is avoided since now
the second locking element is arranged in a separate guide sleeve.
Further, the fixing of the top sleeves of the guide tubes may take place
individually as the guide sleeves are inserted, one by one, through the
holes in the top tie plate.
An additional improvement of the invention is obtained if seats for the top
sleeves are arranged around the holes, into which seats the top sleeves
can be easily guided and fixed, one by one, to the top tie plate by means
of guide sleeves.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be most readily understood with reference to the
accompanying FIGS. 1-6, wherein FIG. 1 schematically shows a fuel assembly
and FIG. 2 is an enlargement of detail 6 in FIG. 1. FIG. 3 shows a
cross-section of the upper part of a top sleeve, FIG. 4 of a guide sleeve
and FIG. 5 of an associated locking sleeve. FIG. 6 shows an alternative
embodiment of the guide sleeve.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1, 1 designates the fuel assembly, which is composed of a large
number of long fuel rods retained by spacer lattices 2. Between the fuel
rods 1 there are arranged guide tubes 3, which are also kept in
predetermined positions by the spacer lattices 2. The guide tubes 3, which
are somewhat longer than the fuel rods 1 and extend somewhat above and
below the ends of the fuel rods, are fixed to the top tie plate 4 and the
bottom tie plate 5. The detail 6, which shows the upper part of the
attachment of a guide tube 3 to the top tie plate 4, is shown enlarged in
FIG. 2.
In FIG. 2, the upper end of the guide tube 3 is joined to a top sleeve 7 by
means of a number of beads. The upper end 8 of the top sleeve 7 is
somewhat reinforced and inside of this part a peripheral slot 9 is
arranged. This corresponds to the previously mentioned first locking
element. Through the top tie plate 4 a hole 10 is provided. Through this
hole there is inserted from above a guide sleeve 11 provided with a flange
12. This guide sleeve 11 is provided with a bead 13 surrounding the sleeve
11, this bead 13 constituting the mentioned second locking element. The
bead 13 is to fit into the slot 9. The guide sleeve 11 is also provided
with a slit 14 (see FIG. 4). A locking sleeve 15 is inserted into the
guide sleeve 11. Further, a seat 16 for the top sleeve 7 is bored in the
top tie plate 4. In FIG. 6 the bead 13 of the guide sleeve has been filled
up.
FIG. 3 shows the upper part 8 of the top sleeve 7 with the slot 9. FIG. 4
shows the guide sleeve with the slit 14 and FIG. 5 the locking sleeve 15.
The mounting operation is carried out such that the top tie plate 4 is
placed on the guide tubes 3 so that the upper ends 8 of the top sleeves 7
are guided into the seats 16.
Then a guide sleeve 11 is pressed down through the hole 9, whereupon the
guide sleeve, because of the slit 14, rebounds so that it enters the hole
in spite of the bead 13. It is pressed in so far that the bead falls down
into the slot 9, the guide sleeve 11 and the top sleeve 7 thus being
locked to each other. The length of the guide sleeve 11 is then adapted
such that, at the very moment when the bead 13 falls down into the slot 9,
the flange 12 impinges against the upper part of the top tie plate 4. In
this way a stable locking of the top tie plate 4 to the guide tubes 3 is
achieved. To prevent the bead 13 from being pulled out of the slot 9, a
locking sleeve 15 is then inserted into the guide sleeve 11. In this way
the first locking element, the slot 9, is interlocked to the second
locking element, the bead 13. To ensure that also the locking sleeve 15 is
not detached, it can be secured by a swelling (not shown) over the bead 13
or below the sleeve 11 in those cases where the bead 13 according to FIG.
6 is not filled.
It would, of course, be possible to have other forms of locking elements
between the top sleeve and the guide sleeve, such as, for example,
different forms of resilient hooks or the like.
When the top tie plate is to be removed, first the locking sleeves 15 and
then the guide sleeves 11 are removed. Thereafter, the top tie plate 4
rests completely freely on the top sleeves 7 of the guide tubes 3.
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